I'm not sure that his departure is as much of a forgone conclusion as some think.
As already covered, for the amount of money it would take to get him, there is a very limited pool of clubs that would pay that. I don't think he's a big enough name for the big boys (L'Pool, Manchesters, Arsenal, Chelsea) to come in for. I would be relatively worried about Leicester if they move someone on, or Villa if Grealish moves.
It really all depends on Matheus himself. If he decides to kick up a stink, we may be left with no choice. As it stands, I think we have a more than decent chance of selling him on the Norwich model and subsequent success for next season.